Zek'vir is the secret final boss of the delves. He has his own delve called Zek'virs Lair in the deepest part of the City of Threads and it consists of a single boss fight against him. Datamining indicates the fight goes up to tier 5 but walking into the delve only lets you see the tiers '?' and '??'.
His fight involves a series of mechanics that can easily oneshot you if you are not properly geared for it and require you to use big part of your defensive and utility kit to deal with it. You aren't required to do a heavy amount of healing here but do need to handle each mechanic almost perfectly while keeping yourself healthy or you will die very quickly
Zek'vir's abilities
Note: This are his abilities on tier 1, he gains new ones as you go up the difficulty levels. Guide will be updated as i progress through them.
First there is 450451. This is a very obvious frontal cone and all you need to do is move out of it. Sometimes he will cast it twice back to back so keep an eye out for that. 450519 works similarly, it includes a grip but the end result if you get hit by it is the same: you die.
450492 creates an aoe circle around Zek'vir that will fear anyone inside once the cast finishes. It is very easy for you to dodge but note that Brann will get feared part of the time, you can opt to dispell him to get him back to doing damage but be very carefull about using your nat because it's vital that you use it properly for the next mechanic.
450505 will apply a nature damage debuff on you and Brann, doing a heavy amount of damage. Brann won't have troubles surviving on his own but you need to dispell this from yourself as soon as possible to avoid the combination of this damage and the melee attacks from killing you. You can also interrupt this cast and Brann will get several interrupts by himself but as a healer it's better for you to let the channel through and heal yourself after because not having your interrupt avaliable might lead you a wipe.
Zek'vir will cast 450568. This spawns a 224077 that can be attacked and does a 15 seconds channel. At the end of the channel if the 224077 is not killed it will spawn a Web Terror that has the abiliy 450597. If this cast goes off it will surely deal to a wipe with no way of recovering
Depending on your item level it is very likely that you simply aren't able to kill the 224077 in time considering you have to keep dodging mechanics and healing yourself. If Brann decides to swap targets and unload a strong hitting ability it will die but otherwise you are bound to get Web Terrors during the fight. This is why it's very important for you to have your interrupt avaliable as having a Terror spawn when you can't interrupt the ability will simply kill you
450597 has to be interrupted. Canceling the cast with something else will just lead to the Terror recasting it instantly.
TL;DR:
- Move out of 450451, 450519 and 450492
- Don't interrupt 450505, let it cast and dispell yourself as soon as possible after
- Try to kill the 224077, if Brann doesn't help you and the Web Terror spawns, interrupt 450597 and kill it as quickly as possible
- Keep yourself and Brann healthy, you will be tanking the boss and if you die the encounter resets